Thermoplastic Polyurethane Film and Preparation Method Thereof

ABSTRACT

A thermoplastic polyurethane film including a cured product of a polyurethane resin composition is provided. The polyurethane resin composition includes a polyurethane resin, a first isocyanate-based curing agent, and an organic solvent. The thermoplastic polyurethane film has a tensile strength of 0.2 MPa to 1.5 MPa at an initial elongation of 5% to 10%. A method for preparing the thermoplastic polyurethane film is also provided.

TECHNICAL FIELD

The present specification claims priority to and the benefit of KoreanPatent Application No. 10-2017-0033596 filed in the Korean IntellectualProperty Office on Mar. 17, 2017, the entire contents of which areincorporated herein by reference.

The present invention relates to a thermoplastic polyurethane filmhaving low stress at an initial elongation, and a preparation methodthereof.

BACKGROUND ART

A thermoplastic polyurethane (TPU) film is excellent in mechanicalproperties such as strength, stretch characteristics, toughness, andabrasion resistance, and thus has been mainly used in the automobilefield.

In general, a polyurethane solution is prepared by dissolving anextruded and molded polyurethane pellet in a solvent, and athermoplastic polyurethane film is prepared by applying the polyurethanesolution onto a substrate. However, since a polyurethane pellet having ahigh molecular weight is not dissolved well in a solvent, a content of asolid content of a polyurethane solution prepared is about 15% or less,which is a low value. Since a polyurethane solution having a low contentof the solid content may not be applied onto a substrate to have apredetermined thickness or more, there is a problem in that it isdifficult to prepare a thick polyurethane film. Further, since it isdifficult to carry out an additional polymerization reaction on apolyurethane pellet, there are problems in that it is not easy tocontrol physical properties of a thermoplastic polyurethane filmprepared from a polyurethane solution, and it is necessary to use ahighly toxic solvent in order to dissolve a polyurethane pellet having ahigh molecular weight.

Meanwhile, in order to apply a thermoplastic polyurethane film to partsof an automobile, engineering parts, and the like, a process ofprocessing the thermoplastic polyurethane film into a curved surface,and the like is required. Thus, there is a need for a thermoplasticpolyurethane film which has a larger thickness and is easily processed.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

The present invention has been made in an effort to provide athermoplastic polyurethane film which has a large thickness and iseasily processed due to low stress at an initial elongation, and apreparation method thereof.

However, a technical problem to be solved by the present invention isnot limited to the aforementioned problem, and the other problems thatare not mentioned may be clearly understood by a person skilled in theart from the following description.

Technical Solution

An exemplary embodiment of the present invention provides athermoplastic polyurethane film including: a cured product of apolyurethane resin composition which includes a polyurethane resin, afirst isocyanate-based curing agent, and an organic solvent, in whichthe thermoplastic polyurethane film has a tensile strength of 0.2 MPa to1.5 MPa at an initial elongation of 5% to 10%.

Another exemplary embodiment of the present invention provides a methodfor preparing a thermoplastic polyurethane film, the method including:preparing a polyurethane resin composition including a polyurethaneresin, a first isocyanate-based curing agent, and an organic solvent;forming a polyurethane resin layer by applying the polyurethane resincomposition onto a substrate film and heat-treating the polyurethaneresin composition; and additionally curing the polyurethane resin layer.

Advantageous Effects

The thermoplastic polyurethane film according to an exemplary embodimentof the present invention has a tensile strength of 0.2 MPa to 1.5 MPa atan initial elongation of 5% to 10%, and has an advantage in that theprocessability thereof is excellent due to low stress at an initialelongation.

The method for preparing a thermoplastic polyurethane film according toan exemplary embodiment of the present invention may prepare athermoplastic polyurethane film which is easily processed due to lowstress at an initial elongation.

The effects of the present invention are not limited to theabove-described effects, and effects, which are not mentioned, will beclearly understood by a person skilled in the art from the specificationof the present application and the accompanying drawings.

BEST MODE

Throughout the specification of the present application, when one part“includes” one constituent element, unless otherwise specificallydescribed, this does not mean that another constituent element isexcluded, but means that another constituent element may be furtherincluded.

Throughout the specification of the present application, when one memberis disposed “on” another member, this includes not only a case where theone member is brought into contact with another member, but also a casewhere still another member is present between the two members.

Throughout the specification of the present application, the unit “wt %”may mean a weight ratio of a component included in a member based on thetotal weight of the member.

Throughout the specification of the present application, the unit “partby weight” may mean a weight ratio between the respective components.

Throughout the specification of the present application, the term“polymerization unit” may mean a form in which monomers react in apolymer, and specifically, may mean a form in which the polymer issubjected to a polymerization reaction to form a skeleton of thepolymer, for example, a main chain or a side chain.

Throughout the specification of the present application, “a weightaverage molecular weight” and “a number average molecular weight” of acompound may be calculated by using a molecular weight and a molecularweight distribution of the compound. Specifically, a sample specimen inwhich a concentration of a compound is 1 wt % is prepared by puttingtetrahydrofuran (THF) and the compound into a 1-ml glass bottle, astandard specimen (polystyrene) and the sample specimen are filteredthrough a filter (pore size of 0.45 mm), and then the elution time ofthe sample specimen is compared with the calibration curve of thestandard specimen by injecting the specimens into a GPC injector,thereby obtaining the molecular weight and the molecular weightdistribution of the compound. In this case, Infinity II 1260(manufactured by Agilent Inc.) may be used as a measuring apparatus, andthe flow rate and the column temperature may be set to 1.00 mL/min and40.0° C., respectively.

Hereinafter, the present specification will be described in more detail.

An exemplary embodiment of the present invention provides athermoplastic polyurethane film including: a cured product of apolyurethane resin composition which includes a polyurethane resin, afirst isocyanate-based curing agent, and an organic solvent, in whichthe thermoplastic polyurethane film has a tensile strength of 0.2 MPa to1.5 MPa at an initial elongation of 5% to 10%.

The thermoplastic polyurethane film according to an exemplary embodimentof the present invention has a tensile strength of 0.2 MPa to 1.5 MPa atan initial elongation of 5% to 10%, and has an advantage in that theprocessability thereof is excellent due to low stress at an initialelongation.

According to an exemplary embodiment of the present invention, thethermoplastic polyurethane film may have a tensile strength of 0.2 MPato 0.5 MPa at an elongation of 5% and a tensile strength of 0.4 MPa to1.5 MPa at an elongation of 10%. Specifically, the thermoplasticpolyurethane film may have a tensile strength of 0.25 MPa to 0.45 MPa,0.3 MPa to 0.4 MPa, 0.2 MPa to 0.3 MPa, or 0.35 MPa to 0.45 MPa at anelongation of 5%. Further, the thermoplastic polyurethane film may havea tensile strength of 0.5 MPa to 1.25 MPa, 0.7 MPa to 1.1 MPa, 0.4 MPato 0.7 MPa, or 0.85 MPa to 1.25 MPa at an elongation of 10%.Accordingly, the thermoplastic polyurethane film may be easily processedthrough a relatively small external force, due to a small tensilestrength at an initial elongation.

According to an exemplary embodiment of the present invention, thethermoplastic polyurethane film may have excellent durability.Specifically, the thermoplastic polyurethane film may have a tensilestrength at break of MPa to 45 MPa. The thermoplastic polyurethane filmsatisfying a tensile strength at break within the above-described rangehas an advantage in that absorption of impact from external force anddurability are excellent.

Accordingly, the thermoplastic polyurethane film may have excellentprocessability due to a low tensile strength at an initial elongation,and may have excellent durability due to a high tensile strength atbreak.

According to an exemplary embodiment of the present invention, a contentof the first isocyanate-based curing agent may be 2.5 parts by weight to5 parts by weight or 3 parts by weight to 5 parts by weight, based on100 parts by weight of the polyurethane resin. By adjusting the contentof the first isocyanate-based curing agent within the above-describedrange, it is possible to implement a thermoplastic polyurethane filmhaving a tensile strength of 0.2 MPa to 1.5 MPa at an initial elongationof 5% to 10%. That is, by adjusting the content of the firstisocyanate-based curing agent in the polyurethane resin compositionwithin the above-described range, it is possible to implement athermoplastic polyurethane film having excellent processability.

According to an exemplary embodiment of the present invention, the firstisocyanate-based curing agent may include two to six isocyanatefunctional groups. For example, the first isocyanate-based curing agentmay include at least one of H12MDI which is a bifunctionalisocyanate-based curing agent manufactured by Evonik Industries, MHG-80Bwhich is a hexafunctional isocyanate-based curing agent manufactured byAsahi Kasei Chemicals Corporation, MFA-100 which is a hexafunctionalisocyanate-based curing agent manufactured by Asahi Kasei ChemicalsCorporation, and TKA-100 which is a trifunctional isocyanate-basedcuring agent manufactured by Asahi Kasei Chemicals Corporation.

According to an exemplary embodiment of the present invention, thepolyurethane resin may be a copolymer of a mixture including: a polyolhaving a number average molecular weight of 1,800 g/mol to 2,200 g/mol;a chain extender including a diol having 4 to 10 carbon atoms; and asecond isocyanate-based curing agent.

According to an exemplary embodiment of the present invention, thepolyurethane resin may be a block copolymer including a soft segment anda hard segment. Specifically, the soft segment of the polyurethane resinmay include a polymerization unit derived from the polyol and the secondisocyanate-based curing agent, and the hard segment of the polyurethaneresin may include a polymerization unit derived from the chain extenderand the second isocyanate-based curing agent.

According to an exemplary embodiment of the present invention, thepolyol may have a number average molecular weight of 1,800 g/mol to2,200 g/mol, 1,950 g/mol to 2,050 g/mol, or 1,900 g/mol to 2,100 g/mol.When the number average molecular weight of the polyol is within theabove-described range, a thermoplastic polyurethane film havingexcellent processability may be implemented due to a low tensilestrength at an initial elongation. Further, by adjusting the numberaverage molecular weight of the polyol within the above-described range,it is possible to suppress the elongation of the thermoplasticpolyurethane film from being decreased.

According to an exemplary embodiment of the present invention, thepolyol may include a diol containing two hydroxyl groups. Specifically,the polyol may include one or more of polycarbonate diol,polycaprolactone diol, polyester diol, and polyether diol.

According to an exemplary embodiment of the present invention, a contentof the polyol may be 60 wt % to 75 wt % based on the weight of themixture. Specifically, the content of the polyol may be 62.5 wt % to 73wt %, 65 wt % to 71 wt %, or 68 wt % to 74.5 wt %, based on the weightof the mixture. By adjusting the content of the polyol in the mixturewithin the above-described range, a thermoplastic polyurethane filmhaving a low tensile strength at an initial elongation may be prepared.Further, by adjusting the content of the polyol within theabove-described range, a content of a hard segment included in thepolyurethane resin is suppressed from being excessively increased, sothat it is possible to prevent a tensile strength at an initialelongation of the thermoplastic polyurethane film from being increased.

According to an exemplary embodiment of the present invention, the chainextender may include a diol having 4 to 10 carbon atoms, or a diolhaving 4 to 6 carbon atoms. A chain extender including the diol havingcarbon atoms within the above-described range may effectively extend thechains of the second isocyanate-based curing agent. Specifically, thechain extender may include at least one of 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 1,10-decanediol,1,1-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol.

According to an exemplary embodiment of the present invention, a contentof the chain extender may be 5 wt % to 10 wt %, specifically, 5 wt % to8 wt %, or 6 wt % to 7.5 wt %, based on the weight of the mixture. Byadjusting the content of the chain extender in the mixture within theabove-described range, the weight average molecular weight of thepolyurethane resin may be improved, and a tensile strength at an initialelongation of the thermoplastic polyurethane film may be suppressed frombeing increased.

According to an exemplary embodiment of the present invention, thesecond isocyanate-based curing agent may include two to six isocyanatefunctional groups. Specifically, the second isocyanate-based curingagent may include two isocyanate functional groups. For example, thesecond isocyanate-based curing agent may include at least one ofisophorone diisocyanate (IPDI), methylenediphenyl-4,4′-diisocyanate,4,4′-methylenebiscyclohexyl diisocyanate, xylene diisocyanate (XDI),naphthalene-1,5-diisocyanate, and cyclohexane diisocyanate.

According to an exemplary embodiment of the present invention, a contentof the second isocyanate-based curing agent may be 20 wt % to 30 wt %based on the weight of the mixture. Specifically, the content of thesecond isocyanate-based curing agent may be 20.5 wt % to 27.5 wt %, wt %to 25 wt %, or 22.5 wt % to 25 wt %, based on the weight of the mixture.By adjusting the content of the second isocyanate-based curing agentwithin the above-described range, a polymerization reaction of thepolyurethane resin may be stably carried out, and a thermoplasticpolyurethane film having low stress at an initial elongation may beprepared.

According to an exemplary embodiment of the present invention, themixture may further include a catalyst. As the catalyst, a catalyst usedin the art may be used without limitation, and for example, dibutyltindilaurate (DBTDL) may be used. Further, the content of the catalyst maybe 0.005 part by weight to 0.02 part by weight or 0.008 part by weightto 0.015 part by weight, based on 100 parts by weight of the mixture.

According to an exemplary embodiment of the present invention, thepolyurethane resin may have the weight average molecular weight of40,000 g/mol to 70,000 g/mol.

By adjusting the weight average molecular weight of the polyurethaneresin, physical properties of the thermoplastic polyurethane film suchas tensile strength and durability may be easily controlled.

According to an exemplary embodiment of the present invention, theorganic solvent may include at least one of acetone, methyl ethylketone, methyl isobutyl ketone, cyclohexane, toluene, xylene, ethyleneglycol monomethyl ether (methyl cellosolve), and ethylene glycolmonoethyl ether (ethyl cellosolve).

According to an exemplary embodiment of the present invention, a contentof the organic solvent may be 30 parts by weight to 80 parts by weightbased on 100 parts by weight of the polyurethane resin. By adjusting thecontent of the organic solvent within the above-described range, acontent of a solid content of the polyurethane resin composition may becontrolled, and coatability of the polyurethane resin composition may beimproved.

According to an exemplary embodiment of the present invention, a contentof a solid content of the polyurethane resin composition may be 20% to70%, specifically, 30% to 60%, or 40% to 55%. In the presentspecification, the “solid content” may mean a solute or a solid materialexcept for the solvent in the entire solution, and specifically, thesolid content of the polyurethane resin composition may collectivelyrefer to the polyurethane resin, the first isocyanate-based curingagent, and an additive such as the catalyst, except for the organicsolvent. When the content of the solid content of the polyurethane resincomposition is within the above-described range, the polyurethane resincomposition may be applied thickly onto a substrate, and accordingly, athermoplastic polyurethane film having a large thickness may beprepared.

According to an exemplary embodiment of the present invention, thethermoplastic polyurethane film may have a thickness of 10 μm to 250 μm.Specifically, the thermoplastic polyurethane film may have a thicknessof 20 μm to 200 μm, or 30 μm to 180 μm. That is, the thermoplasticpolyurethane film may have a large thickness, as compared to an existingpolyurethane film.

Another exemplary embodiment of the present invention provides a methodfor preparing a thermoplastic polyurethane film, the method including:preparing a polyurethane resin composition including a polyurethaneresin, a first isocyanate-based curing agent, and an organic solvent;forming a polyurethane resin layer by applying the polyurethane resincomposition onto a substrate film and heat-treating the polyurethaneresin composition; and additionally curing the polyurethane resin layer.

The method for preparing a thermoplastic polyurethane film according toan exemplary embodiment of the present invention may prepare athermoplastic polyurethane film which is easily processed due to lowstress at an initial elongation. Specifically, the thermoplasticpolyurethane film prepared by the method for preparing a thermoplasticpolyurethane film may have a tensile strength of 0.2 MPa to 1.5 MPa atan initial elongation of 5% to 10%. The thermoplastic polyurethane filmsatisfying a tensile strength at an initial elongation within theabove-described range has an advantage in that the processabilitythereof is excellent.

According to an exemplary embodiment of the present invention, a contentof the first isocyanate-based curing agent may be 2.5 parts by weight to5 parts by weight or 3 parts by weight to 5 parts by weight, based on100 parts by weight of the polyurethane resin. By adjusting the contentof the first isocyanate-based curing agent within the above-describedrange, the tensile strength at an initial elongation of thethermoplastic polyurethane film may be effectively lowered.

According to an exemplary embodiment of the present invention, a contentof a solid content of the polyurethane resin composition may be 20% to70%, specifically, 30% to 60%, or 40% to 55%. When the content of thesolid content of the polyurethane resin composition is within theabove-described range, the polyurethane resin composition may be appliedthickly onto a substrate, and accordingly, a thermoplastic polyurethanefilm having a large thickness may be prepared.

According to an exemplary embodiment of the present invention, thepolyurethane resin used for the method for preparing a thermoplasticpolyurethane film may be prepared by carrying out a copolymerizationreaction of a mixture, which includes: a polyol having a number averagemolecular weight of 1,800 g/mol to 2,200 g/mol; a chain extenderincluding a diol having 4 to 10 carbon atoms; and a secondisocyanate-based curing agent, in an organic solvent.

In addition, the polyol, the chain extender, the first isocyanate-basedcuring agent, the second isocyanate-based curing agent, the organicsolvent, the catalyst, and the like, which are used for the method forpreparing a thermoplastic polyurethane film, may be the same as thepolyol, the chain extender, the first isocyanate-based curing agent, thesecond isocyanate-based curing agent, the organic solvent, the catalyst,and the like in the thermoplastic polyurethane film.

According to an exemplary embodiment of the present invention, thenumber of carbon atoms constituting a diol used as the chain extender isless than the number of carbon atoms constituting the polyol, so thatthe diol in the mixture has a higher fluidity than that of the polyol.Thereby, in the mixture, a reaction of the chain extender and the secondisocyanate-based curing agent may occur earlier than a reaction of thepolyol and the second isocyanate-based curing agent. Specifically, whenbutanediol is used as the chain extender, one hydroxyl group of twohydroxyl groups of the butanediol reacts with and is bonded to anisocyanate group of the second isocyanate-based curing agent, and whilea process of bonding an unreacted hydroxyl group of the butanediol to anew isocyanate group of the second isocyanate-based curing agent isrepeated, a second isocyanate-based curing agent having a long extendedchain structure may be formed. Thereafter, a second isocyanate-basedcuring agent having a long extended chain structure may react with thepolyol to form a polyurethane resin having an increased weight averagemolecular weight.

According to an exemplary embodiment of the present specification, thecopolymerization reaction for preparing a polyurethane resin may becarried out at a temperature of 50° C. to 70° C. By adjusting thecopolymerization reaction temperature within the above-described range,the polyurethane resin may be stably polymerized, and the polyurethaneresin may be polymerized at a relatively low temperature, so thatpreparation cost and preparation time of the thermoplastic polyurethanefilm may be reduced.

According to an exemplary embodiment of the present invention, thecontent of the polyol may be 60 wt % to 75 wt %, 2.5 wt % to 73 wt %, 65wt % to 71 wt %, or 68 wt % to 74.5 wt %, based on the weight of themixture. By adjusting the content of the polyol in the mixture withinthe above-described range, a polymerization reaction of the polyurethaneresin may be stably carried out, and a thermoplastic polyurethane filmhaving a low tensile strength at an initial elongation may be prepared.

According to an exemplary embodiment of the present invention, a contentof the chain extender may be 5 wt % to 10 wt %, 5 wt % to 8 wt %, or 6wt % to 7.5 wt %, based on the weight of the mixture. By adjusting thecontent of the chain extender in the mixture within the above-describedrange, the weight average molecular weight of the polyurethane resin maybe improved, and a tensile strength at an initial elongation of thethermoplastic polyurethane film may be suppressed from being increased.

According to an exemplary embodiment of the present invention, a contentof the second isocyanate-based curing agent may be 20 wt % to 30 wt %,20.5 wt % to 27.5 wt %, 20 wt % to 25 wt %, or 22.5 wt % to 25 wt %,based on the weight of the mixture. By adjusting the content of thesecond isocyanate-based curing agent within the above-described range, apolymerization reaction of the polyurethane resin may be stably carriedout, and a thermoplastic polyurethane film having low stress at aninitial elongation may be prepared.

According to an exemplary embodiment of the present invention, themixture may further include a catalyst. Through the catalyst, apolymerization reaction of the polyurethane resin and a reaction of thepolyurethane resin with the first isocyanate-based curing agent may bepromoted. A content of the catalyst may be 0.005 part by weight to 0.02part by weight or 0.008 part by weight to 0.015 part by weight, based on100 parts by weight of the mixture. By adjusting the content of thecatalyst within the above-described range, a polymerization reaction ofthe polyurethane resin may be effectively promoted, and the polyurethaneresin may be polymerized at a relatively low temperature.

According to an exemplary embodiment of the present invention, thepolymerization reaction of the polyurethane resin may be carried out inan organic solvent. When an aqueous solvent is used in order to preparea thermoplastic polyurethane film, urethane particles need to beprocessed in the form of beads having a diameter ranging from dozens ofnanometers to hundreds of nanometers and dispersed on an aqueoussolvent. In this case, since additives such as various surfactants andmonomers need to be used in order to effectively disperse urethaneparticles on an aqueous solvent, there are problems in that a process ofpreparing the thermoplastic polyurethane film becomes complicated, andpreparation time and preparation cost thereof are increased.

In contrast, according to an exemplary embodiment of the presentinvention, since the polyurethane resin is in a state of being dissolvedin the organic solvent, a dispersion stabilizer-based additive such asan additional dispersant and a surfactant need not be added to thepolyurethane resin composition. Accordingly, preparation time andpreparation cost of the thermoplastic polyurethane film may be reduced.

According to an exemplary embodiment of the present invention, a contentof the organic solvent may be 30 parts by weight to 80 parts by weightbased on 100 parts by weight of the polyurethane resin. By adjusting thecontent of the organic solvent within the above-described range, it ispossible to suppress a phenomenon that the polyurethane resincomposition is rapidly dried in a step of heat-treating the polyurethaneresin composition, so that the organic solvent is swollen, and it ispossible to prevent the thickness of the thermoplastic polyurethane filmfrom being reduced.

According to an exemplary embodiment of the present invention, acomposition including a polyurethane resin and an organic solvent may beprepared by allowing the mixture to react in an organic solvent, and thepolyurethane resin composition may be prepared by adding a firstisocyanate-based curing agent to the composition. That is, the organicsolvent of the polyurethane resin composition may be an organic solventwhich is used during the preparation of the polyurethane resin andremains.

According to an exemplary embodiment of the present invention, thepolyurethane resin may have the weight average molecular weight of40,000 g/mol to 70,000 g/mol. By adjusting the number average molecularweight of the polyol, the number of carbon atoms of the diol used as thechain extender, the content of the polyol in the mixture, the content ofthe chain extender, the content of the second isocyanate-based curingagent, and the like, the weight average molecular weight of thepolyurethane resin may be controlled. By adjusting the weight averagemolecular weight of the polyurethane resin, physical properties of thethermoplastic polyurethane film such as tensile strength and durabilitymay be easily controlled.

According to an exemplary embodiment of the present invention, a methodof applying the polyurethane resin composition onto a substrate film isnot particularly limited, and for example, it is possible to use any onemethod of bar coating, blade coating, slot die coating, spray coating,spin coating, and gravure coating.

According to an exemplary embodiment of the present invention, thepolyurethane resin composition may be applied to a thickness of 20 μm to500 μm on the substrate film. A polyurethane resin layer having athickness of 10 μm to 250 μm may be formed by heat-treating thepolyurethane resin composition applied on the substrate film. In theprocess of heat-treating the polyurethane resin composition, thethickness of the prepared polyurethane resin layer may be reduced as theorganic solvent included in the polyurethane resin composition isvolatilized. Accordingly, the thickness of the polyurethane resincomposition applied on the substrate film may be adjusted inconsideration of the thickness of the polyurethane resin layer that isreduced as the organic solvent is volatilized.

According to an exemplary embodiment of the present invention, athermoplastic polyurethane resin layer may be formed by heat-treatingthe polyurethane resin composition applied on the substrate film at atemperature of 100° C. to 150° C. By heat-treating the polyurethaneresin composition within the above-described temperature range, theorganic solvent included in the polyurethane resin composition may beeffectively volatilized, thereby forming a semi-cured polyurethane resinlayer. Further, by heat-treating the polyurethane resin compositionwithin the above-described temperature range, it is possible to suppressa yellowing phenomenon from occurring in the polyurethane resin layer.

According to an exemplary embodiment of the present invention, thepolyurethane resin layer may be additionally cured at a temperature of25° C. to 40° C. for 48 hours to 72 hours. Since a polyurethane resinlayer formed by heat-treating the polyurethane resin composition is in asemi-cured state, a finally cured thermoplastic polyurethane film may beprepared by additionally curing the polyurethane resin layer.

In the process of additionally curing the polyurethane resin layer, apolyurethane resin included in the polyurethane resin layer and thefirst isocyanate-based curing agent may react with each other, or smallamounts of the polyol, the chain extender, the first isocyanate-basedcuring agent, and the second isocyanate-based curing agent, whichremain, may react with one another, thereby providing a thermoplasticpolyurethane film including a polyurethane resin having an increasedweight average molecular weight.

According to an exemplary embodiment of the present invention, thepolyurethane resin and the first isocyanate-based curing agent mayeffectively react with each other by additionally curing thepolyurethane resin layer under the above-described temperature and timeconditions.

According to an exemplary embodiment of the present invention, thethermoplastic polyurethane film may have a thickness of 10 μm to 250 μm.Specifically, the thermoplastic polyurethane film may have a thicknessof 20 μm to 200 μm, or 30 μm to 180 μm.

According to an exemplary embodiment of the present invention, themethod may further include, after the additionally curing of thepolyurethane resin layer, removing the substrate film. That is, throughthe method for preparing a thermoplastic polyurethane film, a laminatein which a thermoplastic polyurethane film is laminated on a substratefilm may be prepared, and a thermoplastic polyurethane film having lowstress at an initial elongation may be provided by removing thesubstrate film.

Mode For Invention

Hereinafter, the present invention will be described in detail withreference to Examples for specifically describing the present invention.However, the Examples according to the present invention may be modifiedin various forms, and it is not interpreted that the scope of thepresent invention is limited to the Examples to be described below. TheExamples of the present specification are provided for more completelyexplaining the present invention to the person with ordinary skill inthe art.

EXAMPLE 1

Preparation of Polyurethane Resin Composition

Polycarbonatediol (PCDL, Asahi Kasei Chemicals Corporation) having anumber average molecular weight of 2,050 g/mol as a polyol,1,4-butanediol (1,4BD, manufactured by BASF SE) as a chain extender,H12MDI (manufactured by Evonik Industries) including two isocyanatefunctional groups as a first isocyanate-based curing agent, isophoronediisocyanate (IPDI, manufactured by Evonik Industries) as a secondisocyanate-based curing agent, dibutyltin dilaurate (DBTDL) as acatalyst, and methyl ethyl ketone as an organic solvent were prepared.Thereafter, a mixture in which a content of the polyol was about 70.03wt %, a content of the chain extender was about 6.64 wt %, and a contentof the second isocyanate-based curing agent was about 23.33 wt % wasprepared, and a mixed solution was prepared by mixing 100 parts byweight of the mixture and about 50 parts by weight of the organicsolvent.

The prepared mixed solution was charged into a reactor and warmed to 55°C., and 0.005 part by weight of the catalyst was added to 100 parts byweight of the mixture while maintaining the temperature. Thereafter, acomposition including a polyurethane resin having the weight averagemolecular weight of about 51,000 g/mol was prepared by allowing theresulting mixture to react at 57° C. for 25 hours. Thereafter, by addingabout 3 parts by weight of the first isocyanate-based curing agent basedon 100 parts by weight of the prepared polyurethane resin to thecomposition, a polyurethane resin composition was prepared. A content ofa solid content of the prepared polyurethane resin composition was about45%.

Preparation of Thermoplastic Polyurethane Film

The prepared polyurethane resin composition was applied to a thicknessof about 200 μm onto a polyethylene terephthalate (PET) film which is asubstrate film. Thereafter, by heat-treating the polyurethane resincomposition at 100° C., a polyurethane resin layer was formed, and byadditionally curing the polyurethane resin layer at 40° C. for 48 hours,a thermoplastic polyurethane film having a thickness of 95 μm wasfinally prepared.

EXAMPLES 2 to 5

A thermoplastic polyurethane film was prepared in the same manner as inExample 1, except that in order to prepare a polyurethane resincomposition, a polyol, a chain extender, a first isocyanate-based curingagent, a second isocyanate-based curing agent, and a catalyst were usedas in the following Table 1. In the following Table 1, TKA-100 is atrifunctional isocyanate-based curing agent manufactured by Asahi KaseiChemicals Corporation.

COMPARATIVE EXAMPLE 1

A thermoplastic polyurethane film was prepared in the same manner as inExample 1, except that in order to prepare a polyurethane resincomposition, a polyol, a chain extender, a first isocyanate-based curingagent, a second isocyanate-based curing agent, and a catalyst were usedas in the following Table 1. In the following Table 1, MHG-80B is ahexafunctional isocyanate-based curing agent manufactured by Asahi KaseiChemicals Corporation.

TABLE 1 First isocyanate- based curing agent Semi-cured Catalyst (partsby weight) urethane (parts by weight) * Based on 100 parts compositionPolyurethane Chain Second isocyanate- * Based on 100parts by weight ofSolid resin Polyol extender based curingagent by weight of polyurethanecontent Mw (wt %) (wt %) (wt %) mixture resin (%) (g/mol) Example 1 PCDL1,4BD IPDI DBDTL H12MDI 45 52,000 (70.03) (6.64) (23.33) (0.005) (3)Example 2 PCDL 1,4BD IPDI DBDTL H12MDI 46 52,000 (70.03) (6.64) (23.33)(0.005) (5) Example 3 PCDL 1,4BD IPDI DBDTL H12MDI/TKA100 45 52,000(70.03) (6.64) (23.33) (0.005) (3/1) Example 4 PCDL 1,4BD IPDI DBDTLH12MDI 46 51,000 (74.08) (5.34) (20.58) (0.005) (3) Example 5 PCDL 1,4BDIPDI DBDTL H12MDI/TKA100 46 51,000 (74.08) (5.34) (20.58) (0.005) (3/1)Comparative PCDL 1,4BD IPDI DBDTL MHG-80B 45 51,000 Example 1 (52.61)(12.33)  (35.06) (0.005) (5)

Measurement of Tensile Strength of Thermoplastic Polyurethane Film

In order to measure a tensile strength of a thermoplastic polyurethanefilm, samples were manufactured by processing the thermoplasticpolyurethane films prepared in Examples 1 to 5 and Comparative Example 1in accordance with ASTM D-638 standard. Thereafter, by using an ultimatetensile machine (UTM) (Model 3343, manufactured by INSTRON Corp.), anend of the sample was fixed and the other end was pulled at a rate of300 mm/min, and a tensile strength according to the degree to which thethermoplastic polyurethane film was elongated was measured.

The tensile strengths according to the elongations with respect to thethermoplastic polyurethane films prepared in Examples 1 to 5 andComparative Example 1 are shown in the following Table 2.

TABLE 2 Tensile strength (MPa) Elongation of 5% Elongation of 10%Example 1 0.29 1.10 Example 2 0.36 1.21 Example 3 0.46 1.50 Example 40.24 0.44 Example 5 0.27 0.50 Comparative 1.18 2.01 Example 1

Referring to Table 2, it was confirmed that the thermoplasticpolyurethane films prepared in Examples 1 to 5 of the present inventionsatisfied a tensile strength of 0.2 MPa to 1.5 MPa at an initialelongation of 5% to 10%. Specifically, it was confirmed that thethermoplastic polyurethane films prepared in Examples 1 to 5 of thepresent invention satisfied a tensile strength of 0.2 MPa to 0.5 MPa atan elongation of 5%, and a tensile strength of 0.4 MPa to 1.5 MPa at anelongation of 10%. In contrast, it was confirmed that the thermoplasticpolyurethane film prepared in Comparative Example 1 had a tensilestrength of more than 1.5 MPa at an elongation of 10%. Further, it wasconfirmed that the thermoplastic polyurethane film prepared inComparative Example 1 had a tensile strength of more than 0.5 MPa at anelongation of 5%.

Accordingly, it can be seen that the thermoplastic polyurethane filmaccording to an exemplary embodiment of the present invention hasexcellent processability due to a low tensile strength at an initialelongation.

1. A thermoplastic polyurethane film comprising: a cured product of apolyurethane resin composition wherein the polyurethane resincomposition comprises a polyurethane resin, a first isocyanate-basedcuring agent, and an organic solvent, wherein the thermoplasticpolyurethane film has a tensile strength of 0.2 MPa to 1.5 MPa at aninitial elongation of 5% to 10%.
 2. The thermoplastic polyurethane filmof claim 1, wherein a content of the first isocyanate-based curing agentis 2.5 parts by weight to 5 parts by weight based on 100 parts by weightof the polyurethane resin.
 3. The thermoplastic polyurethane film ofclaim 1, wherein the first isocyanate-based curing agent comprises twoto six isocyanate functional groups.
 4. The thermoplastic polyurethanefilm of claim 1, wherein the polyurethane resin is a copolymer of amixture comprising: a polyol having a number average molecular weight of1,800 g/mol to 2,200 g/mol; a chain extender comprising a diol having 4to 10 carbon atoms; and a second isocyanate-based curing agent.
 5. Thethermoplastic polyurethane film of claim 4, wherein a content of thepolyol is 60 wt % to 75 wt % based on the weight of the mixture.
 6. Thethermoplastic polyurethane film of claim 4, wherein a content of thechain extender is 5 wt % to 10 wt % based on a weight of the mixture. 7.The thermoplastic polyurethane film of claim 4, wherein a content of thesecond isocyanate-based curing agent is 20 wt % to 30 wt % based on aweight of the mixture.
 8. The thermoplastic polyurethane film of claim1, wherein a content of a solid content of the polyurethane resincomposition is 20% to 70%.
 9. The thermoplastic polyurethane film ofclaim 1, wherein the thermoplastic polyurethane film has a thickness of10 μm to 250 μm.
 10. A method for preparing the thermoplasticpolyurethane film according to claim 1, comprising: preparing apolyurethane resin composition comprising: a polyurethane resin, a firstisocyanate-based curing agent, and an organic solvent; forming apolyurethane resin layer by applying the polyurethane resin compositiononto a substrate film and heat-treating the polyurethane resincomposition; and additionally curing the polyurethane resin layer. 11.The method of claim 10, wherein the heat treating is carried out at atemperature of 100° C. to 150° C.
 12. The method of claim 10, whereinthe additional curing is carried out at a temperature of 25° C. to 40°C. for 48 hours to 72 hours.
 13. The method of claim 10, wherein thepolyurethane resin is prepared by carrying out a copolymerizationreaction of a mixture, wherein the mixture comprises: a polyol having anumber average molecular weight of 1,800 g/mol to 2,200 g/mol; a chainextender comprising a diol having 4 to 10 carbon atoms; and a secondisocyanate-based curing agent, in an organic solvent.
 14. The method ofclaim 13, wherein the copolymerization reaction is carried out at atemperature of 50° C. to 70° C.